Dental materials have special requirements. For health reasons, dental materials should be suitable for use in the oral environment. In certain applications, strength and durability of a dental material is important to ensure satisfactory performance. For example, for dental work at locations where mastication forces are generally great, high strength and durability is desirable. In other applications, an aesthetic character (e.g., luster and translucency) is desired. This is often the case where dental work is performed at locations where a tooth repair or restoration can be seen from a relatively short distance.
Strength in a dental material is typically achieved by adding fillers. Generally, a dental material has greater mechanical strength when it contains fillers having an average particle size greater than about 0.6 micrometers. A disadvantage of composites with such average particle size is that with repeated toothbrushing (a requirement for oral hygiene), the hardened resin can wear away leaving a dull, unaesthetic surface. The worn surface can be a site for subsequent plaque accumulation.
The use of fillers having an average particle size greater than about 0.6 micrometers also tends to result in dental materials that lack luster and aesthetic character. The matching of refractive indices of the components has been suggested as an approach to improve the visual opacity, and hence the aesthetic character, of such dental materials. However, such an approach restricts the latitude in formulating dental materials by limiting the selection of materials that may be used in the dental materials to those with matching refractive indices.
The use of smaller particles to improve the aesthetic qualities of dental materials is known in the dental arts. For example, dental pastes including non-aggregated silica particles having an average particle size of less than about 200 nanometers have been reported. However, when the loading levels of such fillers are increased to provide the desired mechanical strength upon hardening (e.g., at least about 70% by weight filler in the paste), the resulting pastes are generally sticky. The resulting stickiness of such dental pastes is undesirable for dental practice.
The use of a combination of different average particle size fillers in dental materials has also been disclosed. However, such combinations generally result in dental materials that are lacking in one or more desirable properties. For example, some combinations of different average particle size fillers cannot be loaded into a hardenable resin at high enough concentration to provide dental pastes that have desirable properties, such as mechanical strength upon curing. Other combinations of different average particle size fillers may provide adequate mechanical strength upon curing, but lack desirable aesthetic qualities.
Thus, there is a need in the art for dental pastes that provide a balance of desirable properties.